Asthma is a serious pulmonary disease that is characterized by airway hyper-responsiveness (AHR), airway remodeling, mucus hyper-secretion and airway inflammation. There is considerable information about the pathogenesis of mucus hyper-secretion and airway inflammation. Our knowledge regarding mechanisms of AHR and airway remodeling is limited. Previous studies show that contraction of airway smooth muscle plays a critical role in mediating AHR whereas proliferation of airway smooth muscle cells largely contributes to the pathogenesis of airway remodeling. However, the mechanisms that regulate airway smooth muscle contraction and growth are not well understood. Abl is a nonreceptor tyrosine kinase that is known to regulate the functions of immune cells by controlling actin polymerization, a cellular process that may also regulate contraction of various smooth muscles including airway smooth muscle. Our pilot studies show that Abl is required for airway smooth muscle contraction and growth, suggesting an important role of Abl in airway smooth muscle. The major goal of the project is to characterize the functional role of Abl in airway smooth muscle in vitro and in allergen-induced AHR and airway remodeling in vivo. In Aims 1 and 2, the roles and mechanisms of Abl in regulating airway smooth muscle contraction and growth will be characterized. In Aim 3, the roles of Abl in allergen-induced AHR, airway remodeling and inflammation will be evaluated using an animal model of asthma. Completion of these studies should advance our knowledge regarding smooth muscle contraction/growth and asthma pathology. Obtaining this knowledge may identify Abl as a new biological target for the development of new therapy to treat asthma.